How to Make It
Prepare Cake Layers: Preheat oven to 350°. Stir together sifted cake flour and next 3 ingredients in bowl of an electric stand mixer. Make a well in center of flour mixture; add oil, egg yolks, vanilla extract, and 3/4 cup water. Beat at medium speed 1 to 2 minutes or until smooth.
Beat egg whites and cream of tartar at medium-high speed until stiff peaks form. Fold one-third of egg whites into batter; fold remaining whites into batter. Spoon batter into 4 greased (with shortening) and floured 8-inch round shiny cake pans (about 2 cups batter in each pan).
Bake at 350° for 12 to 14 minutes or until a wooden pick inserted in center comes out clean. (Do not overbake--cakes will be a very pale golden color.) Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely (about 30 minutes).
Prepare Filling: Stir together mascarpone cheese, 1/2 cup powdered sugar, and 1 Tbsp. vanilla in a large bowl just until blended.
Beat 3/4 cup cream at low speed with an electric mixer until foamy; increase speed to medium-high, and beat until soft peaks form. Fold whipped cream into mascarpone mixture until well blended. Add thawed grated coconut, and stir just until blended. Spread mixture between cake layers (about 1 1/3 cups per layer). Cover with plastic wrap, and chill 12 hours.
Prepare White Chocolate Buttercream Frosting: Microwave chopped white chocolate and 2 Tbsp. whipping cream in a microwave-safe bowl at MEDIUM (50% power) 1 to 1 1/2 minutes or until melted and smooth, stirring at 30-second intervals. Cool completely (about 20 minutes).
Beat 1 cup softened butter and 2 cups powdered sugar at low speed with an electric mixer until blended. Add white chocolate mixture, 2 tsp. vanilla, and remaining 1 cup powdered sugar, and beat at high speed 2 to 3 minutes or until fluffy. Spread frosting on top and sides of cake. Cover top and sides of cake with 3 cups flaked coconut, gently pressing coconut into frosting.
Test Kitchen Tip: Be sure to measure flour after sifting. (If you measure before sifting, you'll end up with too much flour and a dry cake.) Check for doneness at the minimum bake time--even 1 or 2 minutes of extra baking can also create a dry cake.
Be sure to measure flour after sifting. (If you measure before sifting, you'll end up with too much flour and a dry cake.) Check for doneness at the minimum bake time--even 1 or 2 minutes of extra baking can also create a dry cake.